1. Field of the Invention
The present invention relates to a battery pack comprising a plurality of battery modules arranged in parallel, each of which has a plurality of cells integrally connected in series, each battery module being cooled in compact structure.
2. Description of the Related Art
Conventionally is known a battery pack with high capacity which comprises a plurality of prismatic cells or battery modules arranged in parallel. Each of the battery modules has a plurality of cells integrally connected in series. A binding rod or a binding band ties the arranged cells or battery modules with end plates disposed at both ends thereof in a parallel direction. In this construction, the cells or battery modules are connected in series.
Japanese Patent Laid-Open Publication No. 2001-167803, for example, discloses a battery pack in which cooling air blows from beneath in an upward direction into between the cells or battery modules of the battery pack. The cooling air prevents increase in cell temperature due to heat generated by charge and discharge, so that it is possible to prevent decrease in battery output, a charge and discharge rate, and battery lifetime.
One example of this type of battery pack will be hereinafter described with reference to FIGS. 7 and 8. In FIG. 7, a battery pack 41 is used as a drive source for an electric vehicle including a hybrid electric vehicle. The battery pack 41 comprises 10 to 30 battery modules 42 arranged in parallel with ventilating spaces 44 in a vertical direction provided between the battery modules 42. A pair of binding bands 46 and a pair of end plates 45 disposed at both ends of the battery modules 42 in a parallel direction hold the battery modules 42 to fix them in an integral manner.
Each battery module 42, as shown in FIG. 8, comprises a plurality of cells 43 integrally arranged in series. Each cell 43 is composed of an electrode plate assembly and an electrolyte solution contained in a case. The plurality of cells 43 are connected in series inside the battery module 42. In the battery pack 41, connection terminals 47 of the battery modules 42, protruding from both end walls thereof, are successively connected in series to obtain a predetermined output voltage of the battery pack 41. Vertical ribs 49 are provided on both sidewalls 48 of the battery module 42 between each of the cells 43 and the ends of the battery module 42, When the battery modules 42 are arranged in parallel in such a manner that the sidewalls 48 of the battery modules 42 are opposed to each other, the vertical ribs 49 make contact with each other to form the ventilating space 44 between the sidewalls 48.
The battery pack 41 is disposed on a bottom chamber 51 which has an air intake space 50 connected with each ventilating space 44. Both ends of each battery module 42 are secured to the bottom chamber 51 with bolts 59 from beneath. A top chamber 53 with an air discharge space 52 is disposed on the battery pack 41. An intake duct 56 connected to an intake fan 55 is fitted into an intake opening 54 provided in an end wall of the bottom chamber 51, and a discharge duct 58 is fitted into a discharge opening 57 provided in an end wall of the top chamber 53.
However, in the battery pack 41 with the above-mentioned structure, the large number of assembly processes and parts are necessary because each battery module 42 is secured to the bottom chamber 51 with the bolts 59, so that cost increases. It is necessary to dispose the end plates 45 at both ends of the arranged battery modules 42, so that the battery pack 41 necessitates a large space for installation and high cost.
To cool each of the battery modules 42, the intake fan 55 supplies the air intake space 50 with air in a vehicle compartment. The air flows through the ventilating spaces 44 between the battery modules 42 from beneath in the upward direction, and is discharged into the air discharge space 52 disposed above the battery pack 41. Accordingly, it is necessary to provide a space for the air intake space 50 and the air discharge space 52. Thus, since the size of the battery pack 41 becomes large in the vertical direction, a place for installation is restricted in a case where the battery pack 41 is used as the drive source for a vehicle.